Mean deviation method of reconnaissance exploration of the earth with radio waves



w. M. BARRET 3,264,555 MEAN DEVIATION METHOD OF RECONNAISSANCE EXPLORATION Aug. 2, 1966 OF THE EARTH WITH RADIO WAVES 5 Sheets-Sheet l Filed Deo. 5l, 1964 T NA 28(|)O0 360.00 Spread to Tra/vsm/'ztef /n fe IN1/mme William M arrel ATTNEYS Aug. 2, 1966 w. M. BARRET 3,264,555

MEAN DEVIATION METHOD OF RECONNAISSANCE EXPLORATION OF THE EARTH WITH RADIO WAVES med Deo. 51, 1964 5 sheets-snm 2 nvm/V701? William N; Bar/ei ATTR/VE'YS g n: -l Aug. 2, 1966 w. m. BARRET 3,'631555 MEAN DEVIATION METHOD OF RECONNAISSANCE EXPLORATION OF THE EARTH WITH RADIO WAVES Flled Dec. 5l, 1964 5 Sheets-Sheet 3 I I .4064@ THM/c IZ\ /7/14/04 /F/EAZS IN1/@M7012 William M. Barei ATTRNEYS United States Patent O $264,555 A MEAN DEVIATION VIETHOD F RECGNNAIS- SANCE EXPLORATIO OF THE EARTH WITH RADIO WAVES William M. Barret, Shreveport, La., assignor to Engineering Research Corporation, Shreveport, La., a corporation of Louisana Filed Dec. 31, 1964, Ser, No. 425,672 4 Claims. (Cl. 324-6) This application is a continuation-impart of my copending application, Serial No. 799,272', filed March 13, 1959, novi/abandoned, for Radio Method of Exploration,l whichI is a continuation-impart of application, Serial No. 328,786, ledDecember 340, 1952, for Method of Radio Exploration.

This invention relates generally to the art of electrical prospecting, and more particularly' to an improved method exploring the earth with radio' waves.

A Applicants U.S. Patent No. 2,172,688 discloses means for' and a method of utilizing radio waves to locate subsurface geologic features, such as an oil deposit. In rder to develop a diagnostic indication of an underlying oil deposit, one of the requirements of the method disclosed therein is that the transmitting means be located to one side of the oil deposit by `a distance that is governled by the depth of the deposit. In searching for wildcat oil accumulations, where neither the presence, location nor depth of the oil is known, it is accordingly necess'ary to position the transmitting means at a large numbei of strategic` locations, so as to be sure o-f occupying the proper position for developing a diagnostic indication of any oil accumulation that may be present. This procedure is so time consuming and costly that the use of the method is restricted largely to outlining oil fields already discovered by drilling but not yet defined in areal extent, land to investigating the oil-producing possibilities of structural prospects'y discovered by geological and/or other geophysical methods. Because of economic considerations, the methoddisclosed in the aforesaid patent is therefore adapted to detail surveying but not to reconnaissance surveying.

One of the objects of the present invention is to provide aradio method Vof exploring the earth which is adapted to rapid and relatively inexpensive reconnaissance investigation-s. K p

Another object is to furnish an effective method of radio exploration which does not require the accurate positioning of the transmitting means.

A further object is to provide a radio method which furnishes electrical indications that may be interpreted statistically in terms of subsurface conditions, thus makingwthe method essentially independent of the technical skill and experience of the interpreter.

An additional object of the instant invention is to make .available apparatus for conveniently and accurately measuring the deviation from normal of the radio observations made in carrying out the herein disclosed method. K

The principle of operation and the application of the instant` invention will be understood fromthe description which follows, together with the appended drawings, wherein:

FIG. l is a diagrammatic plan view of the field layout employed in practicing the preferred method of locating a subsurface geologic feature, such as an oil field.

FIG. 2 is a graph showing the eld intensity observed along' traverse a-b of FIG. 1.

FIG. 3 is a diagrammatic plan view of the field layout employed ir practicing the preferred method of surveyiiig an area dv'id f a geologic feature.

ICC

FIG. 4' is a graph showing the field intensity observe( along traverse c-d of FIG. 3.

FIG. 5 is an opaque sheet having a transparent are: which represents the anomalous area of the graph o: FIG. 2.

FIG. 6 is an opaque sheet having a transparent are: which represents the normal area of the graph of FIG. 2

FIG. 7 is a circuit diagram of the preferred forn of apparatus for comparing areas, such as the transpar ent areas of FIGS. 5 and 6, and thereby measuring th( deviation from normal of recorded data, such as th plotted values of FIG. 2.

In the preferred method of practicing the invention a traverse such as A-B is arranged to cross the area o interest, with the transmitter position t and receiver sta tions r being spaced along the traverse as indicated. f radiortransmitter, such as the continuous wave unmod ulated transmitter described in the aforesaid patent i next set `up at an arbitrary position t and its output pref erably is fed into a radiating means of the characte disclosed in applicants U.S. Patent No. 2,585,907, whicl directs the waves along the receiver traverse a-IJ. Satis factory results have been obtained when radiating 5i watts at any of the 5 geophysical frequencies now as signed by the Federal Communications Commission be tween 1,614 and 1,700 kilocycles per second, but it is t1 be understood that other power levels and other fre quencies will be found suitable for practicing the inven tion. Using a field-intensity measuring device, such a the heterodyne receiver and loop antenna described i; Patent No. 2,172,688, the field intensity of the waves i next determined at each stations from a to b. The sam procedure is then followed for such additional traverse as may be required to explore the area under investiga tion.

The field intensities observed along the reeciver trav erses may next be displayed in the form of graphs, sucl as that appearing in FIG. 2, where the field intensitie measured along receiver traverse a-'b are plotted (eithe manually or with the aid of an X-Y recorder) as ordi nates and abscissas represent the spreads between the re spective receiver stations and the transmitter or other rei erence point, or else they represent the locations of th various receiver stations along the traverse.

Curve, or profile, e-'f is then constructed as the mea curve (as determined visually, or by electronic con puter, or otherwise) for displaying the average variatio with spread of the plotted field-intensity values. Th deviation of each of the plotted values from profile emay next be determined as follows. The deviation t value i is found by dividing the held-intensity interval by the interval k. The same procedure is followed fc each of the plotted values, and the individual deviatior are added, without regard to sign, and divided by tr total number of plotted values appearing in FIG. 2. Tf quotient thus found is the mean deviation of the plotte values from profile e-f. By a similar process, the mea deviation may be found for the field-'intensity values ol served along such other traverses as may be needed 1 explore the area in question, and the mean deviatioi relating to the several traverses may then be average to give the mean deviation for the area explored.

According to the teachings of the present inventio: the magnitude of the mean deviation relating to a pa ticular area provides a criterion for determining whethr `or not the area embraces a subsurface geologic featur for experience has shown that the mean deviation for z area enclosing a geologic feature ordinarily will be si nificantly larger than the mean deviation for an area th is barren of such a feature. Inasmuch as the mean de\ ation varies somewhat from one locality to another, tl

leviation is best evaluated in terms of a geologic feature )y comparing the mean deviation for the area in question vith the mean deviation for a nearby area that is known 'rorn drilling or otherwise to be devoid of such a feature. l`he method of evaluation will be understood fromwhat ollows.

Suppose, for example, that traverseA-B (FIG. l).

)assed over a geologic feature, such as indicated diagramnatical-ly by the outline o, and thatthe mean deviation shown by the data of FIG. 2 is representative of the mean leviation for the area enclosing the 'geologic feature.

uppose, also, vthat traverse C-D (FIG. 3), comprisingv he transmitter position t1 and receiver stations r1, crossed 1 nearby area thatfis barren of a geologic feature; that h-e plotted field-intensity values of FIG. k4 were observed rlong receiver traverse c-d, andfthat the mean deviation )f these values from profile g-h is representative of the nean deviation for the area surveyed.

Actually, traverse A-B crossed over the North Tepetate )il iield of Acadia Parish, Louisiana, and traverse C-D Nas located in a nearby area that is known from drilling o be dev-oid of a geologic feature. It can be shownthat :hemean'deviation for the data of FIG. 2 is 7.67 percent,

1nd that the vmean deviation for the` data of FIG. 4 is 5.15 percent. TheV mean deviationV over the oil fieldis iccordingly 49 percent largerk `than the mean deviation for the barren area.

Despite the fact that the method set forth in Patent No. 2,172,688, as well as the methods disclosed in the prior irt, will not establish the presence ofthe oil iield from heir prescribed treatmentsy of data comparable to that ;hown in FIGS. 2 and 4, it is seen that the herein dis- :losed method does provide an effective statistical techiique of indicating the presence of the. oil field. Morever, this technique is founded on mechanical steps which lo not require experience or technical skill on the part of :heV interpreter.

Surveys conducted in accordance with the method dis- :losed herein have shown that, when a representative number of profiles are obtained over an oil field, and `a representative number of profiles are secured in acom- Jarable area that is barren of a geologic feature, then :the rverage deviation is significantly larger fory the data observed over the oil field. As a result of some 20 field ;urveys carried out over oil fields and a like number of :omparison surveys in barren areas in the same general ocalities, it has been learned that the mean deviation over :he oil fields is of the order -of 50 percent larger than the nean deviation for the barren areas.

Other surveys conducted over diierent types of geoogic features, such as metallic mineral deposits, natural gas deposits, .nonmetallic mineral ydeposits other than Jetroleum and natural gas, salt domes, igneous masses 1nd fault zones, have demonstrated that the presence .of :hese geologic features may also be indicated by the sig riiicant deviation increase they frequently cause. Ordi-. iarily, the largest deviations are observed over oil accunulations and over metallic mineral deposits.

Unlike the method described in Patent No. 2,172,688, :he transmitting means does not have to be accurately vJositioned to one side of the geologic feature under investigation. It preferably should be far enoughremoved rom the feature to permit the propagated radio energy to ;trike the vupper surface of the feature, but near enough Lo keep the receiver readings well above the ambient loise level. Satisfactory results have been obtained ivhen the transmitting means was located to one side .of '.he geologic feature by a spread of from one to ve or nore times the depth of the feature. Inpracticing the Jreferredgmethod of the instant invention, it isnot even iecessary' to know the spread between the transmittingk neansV and the geologic feature surveyed, or the spread Jetween the transmitting means and any of the receiver rtations. Alternatively, the transmitting means may be ocatedmover, rather than to one 4side of, the mineral c deposit or other geologic body'under investigation, and

the receiver traverse :may-overlie .but a portionY of the deposit or body. These desirableffeatures .further dis-V tinguish the, invention fromrthe -methods disclosed in the prior art.

It is eviden-t `from what has gonebefore that themethod disclosed rhere-in is :well adapted to reconnaissancev sufrof a geologic feature is'V indicated ,when the mean devia-5 tion observed al-ong a particular traverse. or traverses, sub-g stantially exceeds the; mean deviationv observed l along an adjacent .traverse `or traverses.. Afterthus determinav ing that' a geologic featureV underlies a particular traverse or traverses, the arealconfigurationof the Vfeaturemay be delineated by `reference Vto vthemost anomalousy seg- Ament of each @profile displaying theV higher deviation.

means of continuous .and `unmodulated .vertically polarr ized sinusoidal'radio waves of'substan-tially constant amf plitude andfrequency,.and` the measurementof the eld Y intensity ofy the.y wavesvwitha. portable Vreceiving means;

which occupiesa series of stations spaced apa-rt from the transmitting means by .successively ,varying.spreads,.,

It will be obvious toone yersed in the art that either the` transmitting means `or ther receiving '.means vmay constitute the stationary or lportable unit, ,or .that both f units lmay bermoved simultaneously, or that either ork both units may be designed for mobile operation;y that Y receiving meansmay be provided for the' continuous meas-- urement of the eld intensity .along vthe freceivertraverse,

rather than for: thev preferred series of measurennentsfaty spaced stations;Y that interrupted .waves may be used in stead of continuous waves; lthatvarious type of modulated waves may be employedv to kreplace the: preferred y.un-

modulated waves; that: different kndslofpolarizations and wave forms may he substituted for .the vertically polarizedsinusoidal Waves speciied,. andI thatVY currents f or pulsesr mayY be :used in place :of theielectromagnetic waves considered herein. Moreover, it will be recognized q that other iield parameters or=characters will vary simulf taneously withV the .iieldr intensity, andthat accordingly the operation of theinvention'may be predicated-on the.;-V

measurement of any selected parameter or characteristic of the electromagneticrfield associatedwith the propagated energy, such as the .area of the lieldV ellipse, :or vits spatial orientation, or the magnitude fof. the; ymajor ior minoraxis of the ellipse, or on the measurement of any selected component of the, resultant field vector,'ori on anyquantity related thereto, suchas the tilt ofthe :wave front.

The operation of `the invention may also beV` based on y phase measurements, which may be made in accordance Vwith the method disclosed in applicants application Serial f No. 106,006, tiled July! 21, 1949, nowl Patent No. :2,901,

688.v acteristicv shall Vtherefore ,be .taken to include= any of In the-claims appendedheretopthe term. chan the iield 'variables here specified, as well asanyother quantity'functionally related to these: eld'variables..

In the preferred method, the transmitting meanspropagates waves, of substantially constant frequency and amv plitude,` but here again it is to be understood.y that. de partures are permissible, for frequencyyariations may ybe followed by a tunabley receiving means, and amplitude. l changes may be compensated forin Various ways,-for

example, by the method Vdisclosed in applicants U.S.

Patent No. 2,573,682.' Furthermore.the preferred method of determining, the deviation of thev measured quantity is to be regarded -asL illustrative rather than,restrictive then dividing the anomalous area by the normal area under the reference curve. The comparison of areas here referred to may be made conveniently by the means described hereinbelow.

With reference to FIG. 5, 4the anomalous area of FIG. 2 is represented on `the sheet 1 by the transparent area 2, which is surrounded by the opaque area 3. Similarly in FIG. 6, the normal area of FIG. 2 is represented on the sheet 4 by the transparent area 5, which is bounded on its upper side by they opaque area 6.

When the anomalous sheet 1 and the normal sheet 4 are placed between like light sources 7 and S (FIG. 7) and like photoelectric cells 9 and 10, the output voltage of the cells 9 will be proportional to the anomalous area 2 of FIG. 5, and the output voltage of the cells 10 will be proportional .to the normal area 5 of FIG. 6.

If the output of cells 9 and 10 be fed into like direct current, logarithmic amplifiers 11 and 12, respectively, then the output voltage of each amplilier will be proportional to the logarithm of its input voltage.

By applying .the outputs of the .amplifiers 11 and 12 to the resistive network that includes the like resistors 13 and 14, the voltage drop across resistor 15 will be proportional to the difference between the logarithmic outputs of the amplifiers 11 and 12, and said voltage drop may be indicated by the voltmeter 16.

If the voltmeter 16 be provided with a logarithmic scale, then its indication will be proportional to the antilogarithm of the difference between the logarithmic outputs of the amplifiers 11 and 12. The voltmeter indication will therefore be proportional to the ratio of the amplifier inputs.

Inasmuch as the transparent area 5 of FIG. 6 will be larger than the transparent area 2 of FIG. 5, it follows that the input to amplifier 12 Will be larger than the input to amplifier 11, so that the indications of voltmeter 16 of FIG. 7 will be proportional to the quotient of -t'he transparent area 5 divided bythe transparent area 2.

As .the reciprocal of this quotient will represent the ratio of transparent area 2 to the transparent area 5, the voltmeter 16 will indicate directly the mean percentage deviation from normal of the recorded values of FIG. 2, or other comparable data under examination, when its scale is properly calibrated in accordance with the reciprocals of its logarithmic indications, as indicated diagrammatically by the scale 17 in FIG. 7.

The preferred apparatus hereinabove disclosed for determining the mean deviation related to profiles, or for comparing areas of other forms, is subject to var-ious modifications. For example, instead of the preferred determination of the mean `deviation of the observed values along the entire profile, the deviation at any -point along the profile may be found by passing the light beams from the light sources 7 and 8 through narrow vertical slits, so as to illuminate only the desired and corresponding parts of sheet 1 (FIG. 5) and sheet 4 (FIG. 6). The reading of voltmeter 16 (FIG. 7) would lthen indicate the percentage deviation at the desired point of the profile.

A further modification of the preferred apparatus of FIG. 7 would be to replace the linear-response photoelectric cells 9 and 10 of FIG. 7 with silicon solar cells which provide output voltages that vary logarithmically with the illumination level, and with this arrangement the output of the solar cells would be fed into linear amplifiers instead of the logarithmic amplifiers 11 and 12.

Moreover, the light beams from light sources 7 and 8 may be modulated in various ways, so that alternating current amplifiers and an alternating current meter may be substituted for the direct current amplifiers 11 and 11 and the direct current meter 16.

Other modifications of the preferred apparatus are apparent, such as the use of an indicating current meter in line 18 of FIG. 7 in place of, or in addition to, tht voltmeter 16, or the use of a recording voltmeter oi current meter, the chart of which would be moved ir synchronism with the progressive and like movement o: sheet 1 and sheet 4 past the light slit referred to above so as to furnish a continuous record of the deviation along the entire length of the profile under investigation.

Although additional modifications of the apparatus wil occur to those versed in the art, it is to be understooc that the preferred apparatus hereinabove disclosed pro` vides a convenient means for determining the mean de` viation from normal of the radio observations used ir carrying out the method of the instant invention, and i performs its function without recourse to any menta steps. It is clear that the preferred apparatus, or obviou: modifications thereof, is suitable for comparing variou: other forms of regular and irregular areas, and accord ingly its use is not restricted to the profile data considerer herein.

It is to be understood therefore that various modifica tions may be made in the method hereinbefore disclosed and in the apparatus referred to for carrying out tht method, without departing from the spirit of the inven tion as defined in the following claims.

I claim:

1. A radio method of locating subsurface geologir features comprising the steps of propagating electromag netic waves along a traverse so that some of said wave are refracted into the earth, measuring a characteristil of said waves at a plurality of locations along said traverse recording the measured values of said characteristil against the location along said traverse at which sait characteristic was measured to obtain a plot of the re corded measurement, constructing the mean curve througl the plotted values, determining the deviation of sai( measured characteristic at each location from said meal curve, determining the average deviation of said measure( characteristic from the mean curve from measurement made in an area known to be void of a geologic feature and determining which of said deviations are significantlj different from said average deviations.

2. The method according to claim 1 in which sait characteristic that is measured is the intensity of th waves, wherein the amplitude and frequency of said wave are maintained substantially constant.

3. The method as defined in claim 1, wherein the sourcof said waves is located to one side of the area unde investigation for the presence of a geologic feature.

4. The method as defined in claim 1, wherein the souro of said waves is located over the area under investigatioi for the presence of a geologic feature.

References Cited by the Examiner UNITED STATES PATENTS 2,172,688 9/1939 Barret 324-1 2,410,550 1l/l946 Pavda 88-1 2,426,918 9/ 1947 Barret 324-1 2,573,682 ll/1951 Barret 324-1 2,578,882 12/1951 EaSh 88-11 2,679,639 5 195 4 Locher.

WALTER L. CARLSON, Primary Examiner.

G. R. STRECKER, Assistant Examiner. 

1. A RADIO METHOD OF LOCATING SUBSURFACE GEOLOGIC FEATURES COMPRISING THE STEPS OF PROPAGATING ELECTROMAGNETIC WAVES ALONG A TRAVERSE SO THAT SOME OF SAID WAVES ARE REFRACTED INTO THE EARTH, MEASURING A CHARACTERISTIC OF SAID WAVES AT A PLURALITY OF LOCATIONS ALONG SAID TRAVERSE, RECORDING THE MEASURED VALUES OF SAID CHARACTERISTIC AGAINST THE LOCATION ALONG SAID TRAVERSE AT WHICH SAID CHARACTERISTIC WAS MEASURED TO OBTAIN A PLOT OF THE RECORDED MEASUREMENT, CONSTRUCTING THE MEAN CURVE THROUGH THE PLOTTED VALUES, DETERMINING THE DEVIATION OF SAID MEASURED CHARACTERISTIC AT EACH LOCATION FROM SAID MEAN CURVE, DETERMINING THE AVERAGE DEVIATION OF SAID MEASURED CHARACTERISTIC FROM THE MEAN CURVE FROM MEASUREMENT MADE IN AND AREA KNOWN TO BE VOID OF A GEOLOGIC FEATURE, AND DETERMINING WHICH OF SAID DEVIATIONS ARE SIGNIFICANTLY DIFFERENT FROM SAID AVERAGE DEVIATIONS. 